A charging War Boar is an ill-tempered mound of bloody-minded muscle with savage tusks and a terrible attitude.
During a turn in which it charged, a War Boar’s Tusks (hand weapon) have a Strength characteristic of S+1 and an Armour Piercing characteristic of -1.
Note that this special rule only applies to attacks made by a War Boar, not to their rider, a chariot or its crew.